I found a good Youtube video on how to disassemble the bottom door and back panel, once inside found a huge (hoooooge) ice ball about 5 inches in diameter encapsulating the defrost thermostat, melted all the ice from the copper line area and thermostat with a hair dryer. The aluminum cooling assembly was clear of frost and ice. I replaced the evaporator fan motor and all is working well now. Not sure why the ice ball formed where it did.